In a Device to Device (D2D) communication system, a node such as device discovers other neighboring node by itself, establishes a communication session with the other node, and then transmits traffic directly to the other node.
Hence, the traffic centralized to a base station is distributed to thus address traffic overload. The D2D communication system is drawing attention as an elemental technology of an advanced mobile communication technology, and a standard group such as 3rd Generation Partnership Project (3GPP) or Institute of Electrical and Electronic Engineers (IEEE) is working on D2D communication standardization based on Long Term Evolution-Advanced (LTE-A) and Wireless Fidelity (WiFi).
A known technology for the D2D communication is FlashLinQ of Qualcomm. The FlashLinQ system defines a physical layer channel structure and a scheduling procedure for the D2D communication, measures a channel quality between the D2D devices for the scheduling, and defines a criterion for the communication based on the channel quality.
In the FlashLinQ system, the device discovers the neighboring device using single-tone signaling. Each device discovers the nearby device within a communication range and transmits a Peer Discovery Resource ID (PDRID) using an Orthogonal Frequency Division Multiplexing (OFDM) symbol in an arbitrary mini-slot in a device discovery interval. The device can discover and identify the neighboring device by demodulating a PDRID of other devices in the mini-slots excluding the above-mentioned mini-slot. However, the device cannot receive the PDRID of the other device in its transmit mini-slot.
For the D2D communication, it is necessary to specify a frame structure, the signaling, and the scheduling for the D2D communication. In the process of the discovery and the scheduling of the D2D communication system, the device receives a plurality of signals overlapping in a time domain from a plurality of devices. When the received signals include a frequency offset, the demodulation performance of the receive signal can deteriorate quite seriously due to a receive Signal to Noise Ratio (SNR) difference between the links between the receiving device and the distributed transmitting devices. To overcome the deterioration, frequency synchronization is required.
Thus, a method and an apparatus for the frequency synchronization in the D2D communication system are demanded.